Rita L. Paldino

Bradykinin-Induced Increase in Total and Effective Blood Flow in Skeletal Muscle

The effect of the synthetic peptide, bradykinin, on total and nutritional blood flow through mammalian skeletal muscle in anesthetized rats, cats, and rabbits was studied. The intra-arterial administration of the drug consistently and significantly increases total blood flow through the gastrocuemius muscle of chloralose-anesthetized cats and rabbits. A similar increase in clearance of the dye “Water Blue” from microinjection sites in the spino-trapezius muscle of the rat and clearance of iodide ions from skeletal muscle in the larger species was established. Bradykinin causes active dilatation of the nutritional circulation as well as increased total blood flow through muscle.

Local Regulation of Effective Blood Flow in Muscle

The techniques of macro- and micro-tissue clearance were used to study reactive hyperemia. Clearance of radioactive iodide from gross injection sites in muscles of rabbits and clearance of micro-injected diffusible dye from the exposed, directly observed spinotrapezius of rats gave evidence for an exact quantitative repayment of effective blood flow debt. In both types of preparation a subnormal clearance followed a thermally induced hyperemia as an apparent compensation. The exact quantitative repayment and compensation support the hypothesis that local effective blood flow is in a steady-state relation to the local concentration in tissue fluid of some agent with vasodilating properties. It is suggested that an extension of this method to studies of vasodilatation induced by drugs or other chemicals might offer an approach to identification of the normal vasodilator, and to physiological proof of its exact nature.

Local Temperature Regulation of Microtissue Clearance from Rat Skeletal Muscle

The influence of local temperature changes on the effective blood flow in the rat spinotrapezius muscle was investigated by the extension of the microtissue clearance technique originally used for frog mesentery. The clearance of water blue from microinjection sites in rat skeletal muscle at 37 C. agrees favorab1y with the clearance of other crystalloid labels from gross injection sites in skeletal muscle of mammalian forms. The data show a direct relationship between clearance rates and temperature over a range of 25 to 45 C. The μ value for clearance agrees with the μ value computed from forearm muscle blood flow measurements, at corresponding temperature ranges.

POSSIBLE ROLE OF THE RETICULOENDOTHELIAL SYSTEM IN PROTEIN TRANSPORT

An individual plasma protein molecule in a living organism may be considered to be simultaneously in three distinct circulations (FIGURE 1). First, it is obviously circulating within the continuous endothelial tubes that constitute the cardiovascular system; second, the proteins of the plasma move in a circuit from the blood to and through the tissue fluid and back to the circulation via the lymphatics; and, third, the protein molecule is in a metabolic cycle that starts with the uptake of its precursors from the environment and ends with the elimination of breakdown products through the kidneys. The possible role of the reticuloendothelial system (RES) in the metabolic breakdown of the plasma proteins has been explored by several workers.’ It has also been suggested that the RES might play a distinct role in the movement of protein from the vascular to the extravascular The rate of movement of the protein molecules in each of these several circuits may be estimated by experimental methods. The movement around the cardiovascular system is measured roughly by the “circulation time.” To distinguish the rate at which proteins move through the blood-tissue fluidlymphatic circuit from the rate at which they are metabolized requires analysis of kinetics of removal of labeled protein from the circulation. The concentration of marked molecules injected into the circulation falls at a rapid nonexponential rate during the early mixing period, then at a somewhat slower, simple exponential rate characterizing the escape of the label from the vascular compartment. This rate remains constant and is measured easily for about 2 hours. At the end of this time the return of labeled protein via the lymphatics is about equal to the rate of disappearance of label from the circulation and a new, slower, exponential removal rate is established, reflecting the metabolic destruction of the labeled protein6 (FIGURE 2). In anesthetized rabbits the rate of disappearance between 30 and 100 min. after injection of Evans blue2 was found to be an acceptable index of the escape of protein from the circulation, for the labeled molecules escaping from the circulation are replaced by largely unlabeled protein molecules from the lymph. Studies of exchange or metabolic breakdown of proteins have generally made use of variously labeled protein molecules. More careful measurements have focused attention on the possible differences between labeled and native protein molecules. The information obtained from many comparisons of different forms of protein labeling strongly suggests that various labels show various degrees of adequacy for studying each of these several phenomena. Partially denatured proteins are removed from the circulation” or are ultimately metabolized’ more rapidly than are carefully labeled, allegedly undenatured proteins. Furthermore, in a recent papers it has been pointed out that although iodinelabeled proteins and Evans blue-labeled proteins are cleared from the blood at * The work reported in this paper was supported in part by Grant H-352 from the National Heart Institute, Public Health Service, Bethesda, Md.

On the mechanism of immunodiffusion

Abstract The present experiments were designed to yield quantitative immunodiffusion data to provide an experimental framework upon which mathematical descriptions of immunodiffusion can be tested. Experiments were carried out over wide ranges of initial amounts of antigen ( M A ) and antibody ( M AB ) employing a new concentric arrangement which allows very precise measurement of the location ( x p ) and time of appearance ( t p ) of the initial zone of precipitation. From experimental data, and using two alternative assumptions about the boudary conditions of the diffusion equation, the concentrations or amounts of antigen and antibody and the antibody-antigen combining ratios in the initial zone of precipitation were computed. It was found that for wide ranges of M A and M AB a linear relationship exists between log M A and x p , and log M AB and x p . A similar relationship was observed between log M A and t p , and log M AB and t p . Within these ranges, use of both types of boundary conditions leads to reasonably consistent values for concentrations or amounts of antibody and antigen in the initial zones of precipitation and yields experimentally reasonable values for antibody-antigen ratios. However, in plates in which M A was very large, unreasonably high antibody-antigen antigen ratios for the initial zone of precipitation were computed. This finding is interpreted as beind due to soluble antigen-antibody complex formation which occurs before the initial zone of precipitation has formed and gives rise to a shift in the location of the initial zone of precipitation toward the antibody well over where it would have occurred had there been no complex formation.

Relationship Between Lymphatic and Blood Flow in Various Structures in the Abdominal Cavity.

Conclusions 1. Clearance of small solutes from the mesentery is about 10 times as rapid as clearance of similar materials from muscle. 2. The ratio of clearances of colloidal to diffusible molecules from mesentery is about 2:3 at 29° and decreases to 1:2.5 at 43°C. 3. Experimentally induced increases of capillary filtration, and presumably lymph formation, increase clearance of colloidal material; those diminishing capillary nitration decrease clearance of colloids. 4. Movement of large molecules from injection depots may serve as an index of local lymph flow; clearance of small diffusible molecules measures flow through vessels capable of exchange. 5. Direct determinations of lymph flow rates from the “iliocolic” duct were found to be almost as great as flow from the thoracic duct. However, occlusion of the “iliocolic” duct diminishes thoracic duct flow by only a very small fraction. This paradox can be explained by the existence of connections between abdominal lymphatics and veins.

Changes in Protein-Bound Dye Disappearance Rate as a Result of Evisceration and Nephrectomy

This study presents data which indicate that evisceration results in a marked decrease in the rate of disappearance of Evans Blue (T-1824) from the circulation of rabbits. Nephrectomy causes a significant increase in the rate of removal of dye from the blood stream. The possible explanations for these changes are considered, and the objections to the use of dye disappearance as a measure of capillary permeability are discussed.